Summary

Conjunctivitis is the inflammation of the conjunctiva, the thin transparent mucous membrane that covers the white of the eye (sclera) and lines the inner surface of the eyelids. It is the most common cause of a red eye in primary care, accounting for approximately 1% of all GP consultations in the UK. [1,2] The classic clinical triad is redness, discharge, and discomfort (grittiness), crucially without significant pain or visual loss. Conjunctivitis is classified by aetiology into three main categories: bacterial (purulent discharge, typically Staphylococcus or Streptococcus), viral (watery discharge, typically adenovirus), and allergic (itching as cardinal symptom, often seasonal). [3] The management is predominantly supportive for viral cases, topical antibiotics (chloramphenicol) for bacterial cases, and antihistamines/mast cell stabilizers for allergic causes. The most critical clinical task is differentiating conjunctivitis from sight-threatening mimics including keratitis (corneal ulcer), uveitis (iritis), and acute angle-closure glaucoma, which require urgent specialist referral. [4]

Key Facts

• Definition: Inflammation of the conjunctiva causing redness, discharge, and discomfort
• Prevalence: 1-2% of GP consultations; lifetime prevalence near 100% [1]
• Incidence: Approximately 6 million cases annually in the UK
• Most Common Cause: Viral (adenovirus) in adults; bacterial in children [2]
• Most Contagious Form: Viral (epidemic keratoconjunctivitis)
• Peak Demographics: All ages; bacterial more common in children, allergic peaks in young adults
• Pathognomonic Feature for Allergic: Itch is the cardinal symptom - no itch makes allergy unlikely
• Gold Standard Investigation: Clinical diagnosis; swabs reserved for atypical cases
• First-line Treatment: Chloramphenicol 0.5% drops for bacterial; supportive for viral
• Prognosis Summary: Excellent - most cases self-limiting within 1-3 weeks

Clinical Pearls

Diagnostic Pearl: "Pain vs Discomfort" - Conjunctivitis causes a gritty, burning, or "sand in the eye" sensation. It does NOT cause deep severe pain. True pain indicates involvement of the sclera (scleritis), cornea (keratitis), or iris (uveitis) and warrants urgent referral.

Examination Pearl: "The Photophobia Test" - Shine a light in the uninvolved eye. If this causes pain in the red eye (consensual photophobia), this is uveitis (iritis), NOT conjunctivitis. Conjunctivitis does not cause consensual photophobia.

Treatment Pearl: Most bacterial conjunctivitis is self-limiting and resolves in 5-7 days without treatment. Antibiotics shorten duration by approximately 1 day and reduce contagiousness. [5]

Pitfall Warning: Any red eye in a contact lens wearer is a corneal ulcer (Pseudomonas keratitis) until proven otherwise. DO NOT treat as simple conjunctivitis - refer to ophthalmology urgently.

Mnemonic: "RED EYE DANGER = Reduced vision, Extreme pain, Discharge purulent + severe, Eye contact lens use, Young neonate, Examining reveals corneal opacity, Deviation of pupil, Asymmetric pupils, No response to treatment in 7 days, Glaucoma symptoms, Eyelid swelling severe, Rash around eye (zoster)"

Why This Matters Clinically

Conjunctivitis is one of the most common presentations in primary care, and correct diagnosis prevents unnecessary antibiotic prescribing (antimicrobial stewardship) while ensuring sight-threatening conditions are not missed. Delayed recognition of keratitis or uveitis can lead to permanent visual impairment. Ophthalmia neonatorum (gonococcal or chlamydial conjunctivitis in newborns) is a notifiable disease that can cause corneal perforation and blindness if not treated promptly. Allergic conjunctivitis significantly impacts quality of life and productivity during peak pollen seasons. From a public health perspective, viral conjunctivitis outbreaks can affect schools and workplaces, requiring appropriate infection control advice.

Structured Approach

General Observation:

• Overall appearance of patient (distress level)
• Evidence of systemic illness (viral upper respiratory tract infection common with viral conjunctivitis)
• Skin examination (vesicles suggest herpes zoster ophthalmicus)

Visual Acuity:

• Essential first step - test with Snellen chart
• Should be normal in uncomplicated conjunctivitis
• Reduced acuity suggests corneal involvement - refer urgently

External Examination:

• Eyelids: oedema, crusting, vesicles
• Periorbital skin: dermatitis, rash
• Preauricular/submandibular lymph nodes: tender, enlarged (viral)

Conjunctival Examination:

• Bulbar conjunctiva: injection pattern (diffuse in conjunctivitis, ciliary flush in uveitis)
• Discharge: purulent, watery, or mucoid
• Chemosis (conjunctival oedema): marked in allergic
• Tarsal conjunctiva (evert lids): papillae, follicles, membranes

Corneal Examination:

• Clarity: should be clear in conjunctivitis
• Fluorescein staining: to exclude corneal ulcer or dendrite (herpes)
• Any opacity = urgent referral

Pupil Examination:

• Size, shape, reactivity
• Abnormality suggests uveitis or glaucoma

Special Tests

Natural History

Most conjunctivitis is self-limiting. Bacterial conjunctivitis typically resolves in 5-7 days without treatment. Viral conjunctivitis may persist for 2-3 weeks, often with fluctuating course. Allergic conjunctivitis persists while allergen exposure continues but is not progressive. Untreated gonococcal or severe bacterial conjunctivitis can progress to corneal ulceration and blindness within 24-48 hours.

Outcomes with Treatment

Prognostic Factors

Good Prognosis:

• Uncomplicated bacterial or viral conjunctivitis
• Normal visual acuity at presentation
• Prompt treatment of bacterial cases
• No underlying ocular surface disease
• Immunocompetent patient

Poor Prognosis:

• Delayed presentation with corneal involvement
• Gonococcal or severe bacterial infection
• Immunocompromised patient
• Underlying dry eye or blepharitis
• Trachoma (in endemic areas - leading infectious cause of blindness globally)

Key Guidelines

1. NICE Clinical Knowledge Summaries (CKS) - Conjunctivitis, Infective (2021) — Most infective conjunctivitis is self-limiting. Topical antibiotics shorten duration by ~1 day. Refer if red flags present. Link

2. Royal College of Ophthalmologists - Ophthalmic Services Guidance (2017) — Red eye referral pathways. Contact lens keratitis requires urgent same-day assessment. PMID: 28764219

3. NICE CKS - Conjunctivitis, Allergic (2022) — Antihistamine drops first-line for seasonal allergic conjunctivitis. Mast cell stabilizers for prophylaxis. Link

4. British National Formulary (BNF) — Chloramphenicol 0.5% drops first-line for bacterial conjunctivitis. Avoid in pregnancy (use fusidic acid).

Landmark Trials

Sheikh A, et al. Cochrane Review (2012) — Antibiotics versus placebo for acute bacterial conjunctivitis

• 11 RCTs, 3,673 participants
• Key finding: Antibiotics associated with faster clinical cure (RR 1.23, 95% CI 1.14-1.34)
• NNT 13 for early clinical cure; most resolve spontaneously
• Clinical Impact: Supports conservative approach; antibiotics optional for mild cases PMID: 22696348

Rietveld RP, et al. (2005) — Predicting bacterial cause in conjunctivitis

• 177 patients with acute conjunctivitis
• Key finding: Glued eyelids in morning and absence of itching best predictors of bacterial cause
• Clinical Impact: Supports clinical differentiation of bacterial vs viral PMID: 15784700

Rose PW, et al. (2005) — Chloramphenicol treatment for acute infective conjunctivitis in children

• 326 children randomized to chloramphenicol vs placebo
• Key finding: No significant difference in cure rate at day 7
• Clinical Impact: Questions routine antibiotic use in children PMID: 16002453

Evidence Strength

What is Conjunctivitis?

Conjunctivitis (also known as "pink eye" or "sticky eye") is inflammation of the thin clear layer that covers the white of your eye and lines your eyelids. Think of it like a skin irritation, but on the surface of your eye. This layer is called the conjunctiva. When it gets irritated or infected, it becomes red and produces discharge, which is why the eye looks pink or red.

Why does it matter?

Conjunctivitis is very common and usually mild. Most cases get better on their own within 1-2 weeks without any lasting problems. However, it's important to see a doctor if: you have significant pain (not just mild irritation), your vision is affected, you wear contact lenses, or if your baby develops eye discharge. These situations need urgent attention to rule out more serious conditions.

How is it treated?

1. Bacterial (sticky, yellow discharge): Antibiotic eye drops from the pharmacy (chloramphenicol) help speed up recovery. Apply as directed, usually for about a week.

2. Viral (watery, clear discharge): Like a common cold of the eye - antibiotics don't help. Keep the eye clean, use cool compresses for comfort, and artificial tear drops if the eye feels dry. It takes about 2-3 weeks to get better.

3. Allergic (very itchy, stringy discharge): Antihistamine tablets (like cetirizine) or antihistamine eye drops help relieve the itching. Avoid the things that trigger your allergy (e.g., pollen, pets).

What to expect

Most conjunctivitis clears up completely within 1-2 weeks (bacterial/allergic) or 2-3 weeks (viral). Viral conjunctivitis may seem to get a bit better, then worse, before finally clearing - this is normal. You can usually continue normal activities, but wash your hands frequently and don't share towels or pillows to avoid spreading it to others.

When to seek help

See a doctor urgently (same day) if:

• You have significant pain in your eye (not just mild irritation)
• Your vision becomes blurry
• Light hurts your eyes (photophobia)
• You wear contact lenses
• Your newborn baby has eye discharge
• The redness is getting worse after a few days of treatment
• There's a white spot on the coloured part of your eye

Common Exam Questions

Questions that frequently appear in examinations:

1. MRCP/Medical Finals: "A 25-year-old woman presents with a 3-day history of bilateral red eyes with watery discharge and tender preauricular lymph nodes. What is the most likely diagnosis?"

2. PLAB/USMLE: "A contact lens wearer presents with a painful red eye and a white spot on the cornea. What is the most appropriate next step?"

3. GP MRCGP CSA: "A mother brings her 3-year-old with sticky eyes, crusted on waking. Describe your examination and management approach."

4. OSCE: "Examine this patient's red eye and describe your findings."

5. Medical Finals SBA: "Which feature most reliably distinguishes allergic from viral conjunctivitis? A) Discharge character B) Itching C) Preauricular lymphadenopathy D) Bilateral involvement"

Viva Points

Opening Statement (How to start your viva answer):

"Conjunctivitis is inflammation of the conjunctiva, the thin mucous membrane covering the sclera and inner eyelids. It is the most common cause of red eye in primary care, presenting with redness, discharge, and grittiness WITHOUT significant pain or visual loss. The three main types are bacterial (purulent discharge), viral (watery discharge, preauricular nodes), and allergic (itching is cardinal feature). The key clinical task is differentiating conjunctivitis from sight-threatening mimics like keratitis, uveitis, and acute glaucoma."

Key Facts to Mention:

• Conjunctivitis is self-limiting in most cases; bacterial resolves in 5-7 days, viral 2-3 weeks
• Antibiotics shorten bacterial conjunctivitis by ~1 day (NNT 13)
• Contact lens wearer with red eye = keratitis until proven otherwise
• Ophthalmia neonatorum is a notifiable disease
• Chloramphenicol 0.5% drops is first-line for bacterial conjunctivitis

Classification to Quote:

• "Conjunctivitis is classified aetiologically as bacterial, viral, or allergic"
• "The presence of follicles suggests viral or chlamydial aetiology; papillae suggest bacterial or allergic"

Evidence to Cite:

• "The Cochrane review by Sheikh et al. (2012) showed antibiotics provide modest benefit for bacterial conjunctivitis with faster clinical cure (RR 1.23)"
• "NICE recommends topical chloramphenicol as first-line for bacterial conjunctivitis"

Structured Answer Framework:

1. Definition and Classification (30 seconds): Define conjunctivitis, three main types
2. Clinical Features (45 seconds): Distinguish bacterial (purulent), viral (watery, nodes), allergic (itch)
3. Red Flags (30 seconds): Pain, photophobia, vision loss, contact lens, neonate, corneal opacity
4. Differential Diagnosis (30 seconds): Keratitis, uveitis, acute glaucoma - how to differentiate
5. Management (45 seconds): Chloramphenicol for bacterial, supportive for viral, antihistamines for allergic
6. Complications and Referral Criteria (30 seconds): When to refer to ophthalmology

Common Mistakes

What fails candidates:

• ❌ Treating all red eyes with topical antibiotics without assessment
• ❌ Forgetting to check visual acuity as the first step
• ❌ Not recognizing contact lens keratitis as an emergency
• ❌ Missing the significance of consensual photophobia (indicates uveitis)
• ❌ Not knowing that itching is the cardinal symptom of allergic conjunctivitis
• ❌ Confusing follicles (pale, viral/chlamydia) with papillae (red, bacterial/allergic)

Dangerous Errors to Avoid:

• ⚠️ Treating a contact lens wearer's red eye as simple conjunctivitis - this may be Pseudomonas keratitis
• ⚠️ Missing ophthalmia neonatorum (gonococcal) - can cause corneal perforation within 24 hours

Outdated Practices (Do NOT mention):

• Routine use of topical steroids in primary care - Risk of viral keratitis and glaucoma
• Silver nitrate prophylaxis for ophthalmia neonatorum - Replaced by topical antibiotics or observation

Examiner Follow-Up Questions

Expect these follow-up questions:

1. "How would you differentiate viral from bacterial conjunctivitis clinically?"

   • Answer: Viral: watery discharge, preauricular lymphadenopathy, follicles on tarsal conjunctiva. Bacterial: purulent sticky discharge, eyelids glued on waking, papillae.

2. "What is the evidence for treating bacterial conjunctivitis with antibiotics?"

   • Answer: Cochrane review (Sheikh 2012) showed modest benefit - faster cure by ~1 day, NNT 13. Most cases self-limiting. Antibiotics reduce contagiousness and may be warranted in children/severe cases.

3. "When would you refer a patient with conjunctivitis to ophthalmology?"

   • Answer: Red flags: severe pain, photophobia, reduced vision, contact lens wearer, corneal opacity, pupil abnormality, neonate, no improvement after 7 days of treatment.

4. "What causes ophthalmia neonatorum and how is it managed?"

   • Answer: Gonococcal (2-5 days, hyperacute, risk of perforation - IV ceftriaxone, saline lavage) or chlamydial (5-14 days, oral erythromycin). It's a notifiable disease requiring urgent ophthalmology referral and contact tracing.

Last Reviewed: 2025-12-26 | MedVellum Editorial Team

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists and current guidelines.